Anchor bolts have been widely used in underground engineering of areas such as mines, hydropower, and transportation. Particularly, using anchor bolts, together with concrete, as permanent support in large underground cavern groups and high slopes has been employed in many engineering projects. An anchor bolt primarily has functions such as suspension, extrusion, and reinforcement, and functions to convert a radially pressing pressure of surrounding rock into a tangential pressure, so as to make use of a bearing capacity of the surrounding rock, strengthen self-stability of the surrounding rock, and prevent a plastic zone of the surrounding rock from being further expanded. Bolting and grouting can reinforce surrounding rock, increase cohesion and an angle of friction of the surrounding rock, and improve the strength of rock, so as to enable the surrounding rock to be cemented into a continuous reinforcement ring and to form an integral support structure system.
Anchor bolt can be classified, according to an anchoring form, into fully grouted anchor bolt, end anchorage type anchor bolt, friction type anchor bolt, and the like, in which the fully grouted anchor bolt is most widely applied. The fully grouted anchor bolt means that an anchor bolt hole is fully filled with an adhesive material, and the adhesive material mainly includes cement slurry, cement mortar, quick-setting cement anchoring agent, resin (including cartridge and resin), and the like. A fully grouted anchor bolt is characterized in that, when the fully grouted anchor bolt is installed, an anchor bolt hole needs to be filled with an adhesive material, so as to enable a gap between a bolt body and a hole wall is densely filled by using the adhesive material, and the bolt body is anchored in rock after the adhesive material is set and hardened. The fully grouted anchor bolt is closely adhered to the hole wall by using the adhesive material. When the rock is deformed, a deformation stress of the rock is transmitted, through the adhesive material, to the anchor bolt to bear, that is, the anchor bolt provides a force for constraining the deformation to the rock, so as to reduce the deformation of surrounding rock.
In anchor bolt design of geotechnical engineering, a length of an anchor bolt is generally 3-6 m. In accordance with a mechanism of action of a fully grouted anchor bolt, after an adhesive material is filled, all parts of the fully grouted anchor bolt that are in contact with rock need to implement functions. However, due to flowability of the adhesive material and a limitation of an installation process, a part of length of the anchor bolt near an opening section fails to completely implement a function, which means that an anchorage length with respect to the rock fails to meet an original design requirement. Therefore, in FIG. 1, an anchor bolt is divided into an extended section, a free section, and an anchoring section. The extended section is secured to a rock wall by using a plate and a nut. The free section is a length that fails to implement a function of the anchoring bolt due to adhesion quality. The anchoring section actually implements a function in the engineering, and an engineering designer concerns the anchoring section most.
To ensure anchoring quality, a relativity large quantity of testing methods appears in engineering. A most common method for testing anchoring quality of an anchor bolt is over-coring an anchor bolt hole. Although this method can soundly test the anchoring quality, the method needs to damage an installed anchor bolt, and the anchor bolt needs to be replaced and installed again after the testing is completed. Later, non-destructive testing methods emerge. Most of the non-destructive testing methods are dependent on approaches such as ultrasound, acoustic emission, and the like. By means of collection of sound and light signals transmitted by a bolt body, a defect of and installation quality of an anchor bolt are determined. However, the foregoing non-destructive testing methods can merely determine installation quality of an anchor bolt, but fail to accurately measure an anchorage length of the anchor bolt.